Method and apparatus for manufacturing an aerosol



T. A. RICH March 10, 1964 METHOD AND APPARATUS FOR MANUFACTURING ANAEROSOL Filed Jan. 17, 1962 [VJ entor 7%e0o0re A. F/a/J fly 4 4 W 6545A'forvvey from higher altitudes.

United States Patent 3,124,442 METHOD AND APPARATUS FOR MANUFAC- TG ANAEROSQL Theodore A. Rich, Scotia, N.Y., assignor to General ElectricCompany, a corporation of New York Filed Jan. 17, 1962, Ser. No. 166,794(Ilairns. ((11. 62-419) releasing the pressure to vaporize the liquid toobtain an aerosol in a fine spray form. Another conventional methodconsists of storing solid particles in a pressurized container andreleasing the pressure to obtain an aerosol of the solid particles. Alimitation'in either of these conventional methods is that the particleswhich com prise the aerosol are not available as discrete particlesbefore they are dispersed in the air. In the liquid spray method thereis no separation of the liquid particles, While inthe solid particlemethod, there is separation but the problem of coagulation of theparticles exists. This inability to obtain discrete particles beforedispersal as an aerosol is a limiting factor in determining the size ofthe particles which are obtained in the aerosol. Thus aerosol particlesproduced by the liquid spray method are small in size when the pressureis first released, at which time the pressure is high, and become largerin size :as the pressure decreases with time. Moreover, the minimum sizeof an aerosol produced by a spray is limited. Theparticles of an aerosolproduced by the solid particle method are likewise irregular in size dueto the problem of coagulation of the individual particles while storedwithin the container.' Further, the inability to store discreteparticles before dispersal as an aerosol,

prevents obtaining an aerosol composed of particles of known uniformsize when this is desired.

Within recent years the science of measuring particles has grown inimportance but no recognized laboratory standard for particle sizemeasurement'exists since no means has been available to store particlesof known uniform size without coagulation during the storage period:.Another area-in which aerosols are important is in crop dusting from anairplane; Conventional crop dusting requires a low flying airplane forproper dispersal of the aerosol over the area to be treated. The releaseof an aerosol at high altitudes allows. it to be carried by the wind andthere is little control on the area treated This need for a low flyingairplane can become a problem if there are obstacles of considerableheight on the ground, in the path of the airplane, and

can also have a possible harmful side'eifeot of frightening animalslocated within close proximity of the crop dusting. Therefore, a needexists tonconduc-t crop dusting Further, in areas such as the field ofmedicine, it may be desired to store particles, both animate andinanimate, in: such a manner as to prevent any interaction between theparticles, or between the particles and the surrounding environment.Finally, the

study of particles is also important in developing filters such as forair conditioning equipment.

Therefore, one of the principal objects of this invention is to developa new and i-mproved'aerosol which can be stored as discrete particlesand will not coagulate over the period of time during storage.

Another object of this invention is to develop a new 3,124,442 PatentedMar. 10, 1964 and improved aerosol in which the particles are of uniformsize.

Another object of this invention is to develop a new and improvedaerosol that can be dispersed from a considerable altitude.

Still another object of this invention is to develop a i new andimproved method and apparatus for producing encapsulated particles arestored by maintaining them at a low temperature during the storageperiod to forestall sublimation of the sheath, and thereby preventcoagulation since the particles are finitely separated from each other.Exposing the encapsulated particles to ambient temperature sublimatesthe solid sheath and causes the particles to become airborne. The methodand apparatus for encapsulating the panticles employs a means in whichthe particles and gaseous carbon dioxide are mixed in a cold air streamto solidify the carbon dioxide about the particle. 'The encapsulatedparticles can be dispersed into the air immediately after they areformed, or they may be collected as amass having the general appearanceof a flufiy mass of snow, then formed into the general shape of asnowball and stored at a low temperat-ure until the aerosol is to bedispersed at which time the snowball is released to the atmosphere.

The features which I desire to protect herein are pointed out withparticularity in the appended claims. The invention itself together withturther objects and advantages thereof, may best be understood byreference to the following description taken in connection with theaccompanying drawings.

FIGURE 1 illustrates an apparatus for encapsulating and collectingaerosol particles.

FIGURE 2 illustrates a modification of the apparatus of FIGURE 1.

Referring particularly to the apparatus illustrated in FIGURE 1, thereis shown a container designated by numeral 1, filled with solid carbondioxide and maintained at ambient temperature. Due to the ambienttemperature, the solid carbon dioxide sublimates and flows into theconduit means 2 in gaseous form. The conduit means may be a glasstubing. The gaseous carbon dioxide then passes through a filter 3 ofconventional design to remove any contaminants which may have beenpresent in the solid carbon dioxide. The filtered gaseous carbon dioxidethen continues on its path through the conduit into the particle chamber4; wherein are located the particles to be encapsulated. A pump 5agitates the particles within the chamber 4to mix the particles with theincoming carbon dioxide, thereby causing a particle laden gaseous carbondioxide stream to flow through conduit 6. Air at ambient conditions ispumped into conduit 7 by means of pump 8. The air passes through a dryer9 of conventional design to remove any moisture in the air which couldsubsequently condense and freeze while passing through a cooling chamberand thereby clog the conduit. The dry air next passes through a filterit) of conventional design to remove any contaminants which might havebeen present in the ambient air and then passes into conduit 11.Conduits 6, 7 and 11 may be made of glass tubing. A first coolingchamber which 'terial such as expanded plastic.

is designated as a whole by the numeral 12, is comprised of a container15, divided into two sections 13 and 14. The container may be made ofmetal or wood or a like material, and is lined with a thermal insulationma- The body of the thermally insulated container 15, is enclosed by acover 16. Conduits 6 and 11 carrying the gaseous carbon dioxideparticlemixture and filtered dry air, are joined to cooling tubes 17 and 18respectively. The cooling tubes may comprise spiral copper tubing toobtain high heat transfer. Within the cooling chamber 12, the space ineach section 13 and 14, surrounding the cooling tubes 17 and 18,contains a cooling medium to cool the gases and particles flowingthrough the cooling tubes. Thus solid carbon dioxide is contained withinspace 13 to lower the temperature of the gaseous carbon dioxide-particlemixture, and liquid nitrogen is contained within space 14 to lower thetemperature of the filtered dry air. The outlets of cooling tubes 17 and18 converge at junction 19, wherein the cold airupon striking the cooledcarbon dioxide-particle mixture, causes the carbon dioxide to solidifyabout each of the particles, thereby encapsulating them. The outlet fromjunction 19 to chamber 20 may be a copper conduit 21 of constantcross-section as shown, or an expansion orifice, the latter resulting ina further reduction in temperature of the encapsulated particles whichmay be necessary under some conditions. The encapsulated particles,having a general appearance of miniature snow flakes, are drawn into asecond cooling chamber 20 which may be a flanged cylinder of glass,sealed at its upper end in any conventional manner to the first coolingchamber 12 by means of the flanged section 22, and open at its lower end23 to permit a vacuum pump 24 to draw a small vacuum thereby pulling theencapsulated particles from the junction 19 at which they were produced.A metal screen 25 having a layer of synthetic fur on its upper sideencloses the lower end of second cooling chamber 20. The encapsulatedparticles are preferably deposited on the synthetic fur rather than thebare metal screen since there is less heat transfer with the fur,therefore, immediate melting of the snow flakes is avoided when the snowladen fur screen is removed to the ambient air. The snow flakes may bedeposited to any desired depth on the fur. A flanged cylindrical'glasscontainer 26 encloses cooling chamber 20, and the lower half of thespace between the two cylindrical surfaces 20 and 26 is filled withsolid carbon dioxide 27, which is maintained at a slightly reducedpressure by the action of the vacuum pump 24 to obtain a lowertemperature and thereby maintain the carbon dioxide which encapsulatesthe particles in a solid state. Flange 28 of container 26 is sealed tothe bottom of cooling chamber 12 in the same manner as flange 22.Alternatively, flange 22 may extend outwardly to the region of flange 28and there be sealed to both flange 28 and the bottom of chamber 12. Aperfect seal is not required at the joint between the bottom of chamber12 and the flanges 22 and 28 since the purpose of this seal is merely topermit the snow flakes to be maintained at a temperature low enough toprevent sublimation of the carbon dioxide while stored on the fur.However, a gasket may be used at this joint if the temperature cannot bemaintained sufliciently low in chamber 20 due to considerable air leaksat the joint. A cylindrical glass wall 29, concentric with the wall ofcontainer 26, is joined to the outer surface of container 26, at itsupper and lower end. This glass wall 29 may extend up to the flange 28and down to the bottom of container 26, even surrounding the bottom ifnecessary. The space 30 between walls 26 and 29, is maintained at avacuum thereby acting as a thermal insulation. snow flakes on the furscreen 25 can be viewed through the glass walls 20, 26, 29 and when anappropriate amount is produced, the flakes may be removed by removingscreen 25, The screen 25 may be removed by The production of 4- any ofseveral methods. The bottom of container 26 may be made removable topermit access to screen 25, or the seal at flange 28 may be opened.Vacuum pump 24 is not intended to create an appreciable vacuum withincontainers 20 and 26, but merely to aid in the flow of the gaseouscarbon dioxide particles and air through the conduits and to draw offthe produced encapsulated particles from junction 19 to prevent cloggingat that point, and also to slightly lower the temperature of the solidcarbon dioxide in region 27 to insure that the particles remainencapsulated while forming a flulfy snow mass on the fur screen. Afterthe snow laden fur screen is removed from chamber 20, the fiufiiy massof snow may be pressed into a generally snowball shape. The encapsulatedparticles in snowball form can be stored for considerable lengths oftime with the asurance that the particles will not coagulate as long asthe snowball is stored at a temperature below K. in the case of carbondioxide encapsulated particles. Thus, if particles of known uniform sizeare available in particle chamber 4, they can be stored in a snowballform and transported to any location which has a need for particles ofknown size. Particles of size down to 5 10 cm. radius may beencapsulated by the method described herein.

The encapsulated particles are released as an aerosol of individualparticles by exposing the snowball to the ambient atmosphere. If thesnowball is released from a considerable altitude, as for crop dusting,the snowball will fall rapidly to the ground and dispersal can takeplace at a selected target. The dispersal from the snowball may be madein a variety of ways. Explosive scattering of the snowball into smallpieces can be done by a powder charge or even by the pressure built upby the subliming solid carbon dioxide. Self dispersal requires acontainer with a small outlet through which the gaseous carbon dioxidestreams with an appreciable velocity that carries the aerosol to theouter air and minimizes the diffusion of water vapor into the container.Self dispersal Without a container is difficult to obtain, since watervapor in the air condenses on the surface of the snowball as it isfalling, and the surface tension restrains the aerosol particles,thereby preventing their escape.

The apparatus in FIGURE 1 therefore produces encapsulated particles bymixing gaseous carbon dioxide and the particles in one flow path of thesystem, introducing filtered dry air into a second flow path of thesystem, separately cooling each flow path and then mixing the output ofboth flow paths whereby the cold dry air causes the carbon dioxide tosolidify and encapsulate the particles. FIGURE 2 illustrates a modifiedapparatus for producing encapsulated particles. In this arrangementfiltered dry air is mixed with the particles, the mixture issubsequently cooled by liquid nitrogen and finally the cold particlestraveling in the cold air stream are mixed with gaseous carbon dioxideand thereby encapsulated.

Referring particularly to FIGURE 2, wherein the numerals identical tothose used in FIGURE 1 represent identical components, filtered dry airis pumped into conduit 11, the pump, dryer, and filter not being shown,

' but being similar to those indicated in FIGURE 1, and

this filtered dry air enters particle chamber 4. The particles to beencapsulated are located in particle chamber 4, and are agitated byblades 31 which are rotated by motor 32. The particle-air mixture thenenters conduit 33 and exists into cooling chamber 34. Liquid nitrogen incontainer 35 is caused to drip into the cooling chamber in the region ofthe conduit 33 outlet, thereby cooling the particle laden airstreamflowing therefrom. Thermal insulation 36 of the type disclosed in FIGURE1 surrounds the cooling chamber 34 and liquid nitrogen container 35.Solid carbon dioxide located in container 1 is caused to sublime due tobeing maintained at ambient temperature and the gaseous carbon dioxideflows into conduit 2, through filter 3 and into the coolingchamber 34wherein it is mixed with the cold particle laden airstream therebycausing the carbon dioxide to solidify about the particles, andencapsulate them. The encapsulated particles, appearing as miniaturesnow flakes, are drawn into a second cooling chamber 20, maintained at alow temperature by solid carbon dioxide 27, and are deposited on furscreen 25 with the aid of vacuum pump 24 in the same manner as disclosedfor the apparatus in FIGURE 1. Storage of the 'encapsulted particles inthe form of a snowball, and its subsequent release to the atmosphereforparticle dispersal as an aerosol is performed in the same manner asdisclosed in the description of FIGURE 1. Flow meters 37 and '38,located in the air and gaseous carbon dioxide conduits, respectively,are useful in determining the amount of encapsulated particles produced.Flow meters could likewise be employed in the conduits 6 and 11 ofFIGURE 1 to indicate the volume of flow therein. All of the conduits andchambers in which there is a gas flow, air or carbon dioxide, arepreferably cylindrical in shape with a minimum of sharp bends in theconduits to aid in the gas flow and prevent collection of any matter onthe sides which would decrease the efiiciency of the system and couldeventually block the flow. The conduits may be made of materials otherthan glass, the only requirement being that the conduit material doesnot react with the gas or particle flow. Copper is indicated as apreferred material in parts of the system Where high heat transfer isdesired. The apparatus illustrated may also be employed to store liquidparticles by forming a snowfall of carbon dioxide and spraying it withliquid droplets as it grows. At ambient temperature the carbon dioxidesublimates and disseminates the frozen droplets.

Having described a new aerosol and a new method and apparatus ofproducing the aerosol in accordance with the invention, it is believedobvious that other modifications and variations of the invention arepossible in light of the above teachings. For example, pumps may beplaced in all of the flow paths and controlled to regulate the resultantproduction of the aerosol. Furthermore, cooling means other than liquidnitrogen may be employed. Also, the encapsulating material is notlimited to carbon dioxide, but may be any material characterized by itscapacity to sublime, an example being camphor. It is obvious thatdifferent temperatures would be required if difiterent encapsulatingmaterials are employed. Finally, the carbon dioxide need not'beinitially in the container 1 in a solid state, but may be available as agas stored in a tank. It is therefore to be understood that changes maybe made in particular embodiments of the invention described which arewithin the full intended scope of the invention as defined by thefollowing claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A method for producing an aerosol comprising the steps ofencapsulating particles of size assmall as 5 X centimeter radius with asheath of solid material which is characterized by its capacity tosublime, and exposing the encapsulated particles to ambient temperaturewhen the aerosol particles are to be released.

2. A method for making particles airborne comprising the steps ofencapsulating aerosol particles of size as small as 5X10- centimeterradius with a sheath of solid material which is characterized by itscapacity to sublime, and exposing the encapsulated particles to ambienttemperature when the aerosol particles are to be released therebysublimating the solid sheath and causing the particles to becomeairborne.

3. A method for preventing coagulation of aerosol particles Whilestoring an aerosol comprising the steps of encapsulating individualparticles of size as small as 5 10' centimeter radius with a sheath ofsolid material which is characterized by its capacity to sublime,

collecting the encapsulated particles in a container maintained at a lowtemperature to prevent sublimation of the solid material, andmaintaining the encapsulated particles at the low temperature during theperiod of storage.

4. A method of'manufacturing an aerosol to be stored comprising thesteps of introducing gaseous carbon dioxide into a flow path of asystem, admitting a filtered dry air stream into another fiow path ofthe system, introducing aerosol particles of size as small as 5 1Ocentimeter radius into oneof the flow paths, mixing the gasous carbondioxide, dry air, and particles, and cooling the mixture to solidify thecarbon dioxide on the particles to form a sheath enclosing theparticles.

5. A method of manufacturing an aerosol comprising the steps ofintroducing gaseous carbon dioxide into a flow path of a system, mixingthe gaseous carbon dioxide with aerosol particles of size as small as 5l0" centimeter radius under controlled conditions, admitting a filtereddry air stream into another flow path of the system, separately coolingthe flow paths of particle laden carbon dioxide and air, and mixing theoutput of both flow paths to solidify the carbon dioxide about theparticles thereby encapsulating them.

6. A method for storing an aerosol comprising the steps of introducinggaseous carbon dioxide into a fiow path of a system, admitting filtereddry air into another flow path of the systems, suspending aerosolparticles of size as small as 5 l0- centimeter radius in the dry airunder controlled conditions, cooling the particles and dry air, mixingthe gaseous carbon dioxide and cooled particles and dry air to solidifythe carbon dioxide on the particles, thereby encapsulating them, andmaintaining the encapsulated particles at a low temperature to preventcoagulation during the storage period.

7. A method of dispersing an aerosol comprising the steps ofencapsulating aerosol particles of size as small as 5X 10- centimeterradius with a sheath of solid carbon dioxide, collecting theencapsulated particles in a container maintained at low temperature toprevent sublimation of the carbon dioxide, forming the collectedencapsulated particles into a generally snowball shape, and exposing thesnowball to atmospheric conditions to permit a dispersal of the aerosolparticles as the carbon dioxide sublimated.

8. Apparatus for producing an aerosol comprising, means for releasing aflow of material characterized by its capacity to sublime into a firstconduit means in gaseous form, means for introducing a flow of filtereddry air into a second conduit means, means for suspending aerosolparticles of size as small as 5X 10" centimeter radius in one of the gasflows, means for cooling at least one of said gas flows, and a commonoutlet means for mixing said gaseous material, filtered dry air, andaerosol particles in a cold atmosphere, thereby encapsulating saidparticles with said solid material within said air stream.

9. Apparatus for producing a carbon dioxide aerosol comprising, acontainer means for releasing carbon dioxide in a gaseous form into afirst conduit means, a chamber under controlled flow pump conditions forsuspending particles of size as small as S lO-' centimeter radius in thegaseous carbon dioxide flow, means for introducing an ambient air streaminto a second conduit means under controlled flow pump conditions, saidair stream being dried and filtered in said second conduit means, acooling chamber container one section for receiving said first conduitmeans with the gaseous carbon dioxide and suspended particles thereinand a second section for receiving said second conduit means with thefiltered dry air stream therein, an outlet means in said cooling chambermaintained at a cold temperature and being connected to the outlets ofboth of said conduit means to mix the cooled carbon dioxide, particlesand air to eifect encapsulation of the particles by solidified carbondioxide, and a second cooling chamber immediately adja- 7 cent to saidoutlet means for capturing and storing said encapsulated particleswithout coagulation.

10. Apparatus for manufacturing an aerosol that is to be stored for atime before dispersal comprising, means for introducing a filtered anddried air flow in a first conduit means, a chamber for agitatingparticles to cause said particles to become suspended in said air flow,means for releasing carbon dioxide in a gaseous form into a secondconduit means, means for mixing the particles and carbon dioxide withinthe air flow, a first cooling means to solidify the carbon dioxide aboutthe particles thereby Y encapsulating them Within said air flow, asecond cooling means adjacent said first cooling means, said secondcooling means preventing sublimation of the carbon dioxide While saidencapsulated particles are being collected, and means for collectingsaid encapsulated particles.

References Cited in the file of this patent UNITED STATES PATENTS1,970,437 Snitkin Aug. 14, 1934 2,570,074 Rupp Oct. 2, 1951 2,601,298Keith June 24, 1952 2,696,718 Garbo Dec. 14, 1954 2,702,091 Smith Feb.15, 1955 2,966,037 Gifford Dec. 27, 1960

1. A METHOD FOR PRODUCING AN AEROSOL COMPRISING THE STEPS OFENCAPSULATING PARTICLES OF SIZE AS SMALL AS 5 X 10**-7 CENTIMETER RADIUSWITH A SHEATH OF SOLID MATERIAL WHICH IS CHARACTERIZED BY ITS CAPACITYTO SUBLIME, AND EXPOSING THE ENCAPSULATED PARTICLES TO AMBIENTTEMPERATURE WHEN THE AEROSOL PARTICLES ARE TO BE RELEASED.